In certain applications, such as light-emitting device (LED) related applications, highly stable and accurate currents are needed. For example, LEDs need highly accurate currents so that the brightness of the LEDs may be accurately controlled. DC-DC converters were commonly used in integrated circuits for providing the accurate currents. In the DC-DC converters, reference voltages free from temperature variations, voltage variations, and process variations are generated, and are then converted to currents, which will also be highly accurate and stable.